Current state-of-the-art semiconductor device processing trends are increasingly moving towards thin film devices, flexible electronics, and sophisticated three-dimensional integration schemes, and the like. All of the aforementioned generally require device layers to be transferred from a growth substrate of one desired property (e.g., a desired lattice parameter) to an alternate substrate with other desired qualities (e.g., for integration with other devices).
Transfer of a device layer from a growth substrate to another substrate may be accomplished by several different methods such as, but not limited to: a lapping and etching process, separation by ion implantation, a laser lift-off method, and a selective etching process. All of the above have limitations which will be described below.
Semiconductor film transfer may be done by a lapping and etching process. With GaAs and InP based materials, the substrate is often removed by lapping and chemical etching after the original wafer is mounted face down on the new substrate. The waste products of this process may be recycled; however significant energy and cost go into the recycling process.
Separation by implantation is used in the Silicon on Insulator (SOI) process, whereby a thin layer of silicon is transferred to an insulating substrate for further processing. This technique has not been applied to other semiconductors or to epitaxial layers that may be damaged by ion implantation.
Laser Lift-off (LLO) has been used successfully by the GaN LED industry for separating the processed devices or the epitaxial film from the sapphire substrate that was used for the epitaxial growth. Laser lift-off may be used with GaN family of materials grown on a sapphire substrate. The substrate may be reused after laser lift-off. The typical process involves irradiating the wafer with short ultraviolet laser pulses through the transparent sapphire substrate. The interfacial GaN layer absorbs the radiation and generates localized heat that facilitates the release of the substrate. This approach, however, is not applicable to III-V substrates (on which most lasers, optoelectronic devices, and many high-speed electronic devices are grown). The reason is that the substrates are opaque to visible and UV radiation. Also no interfacial layer exists that can absorb the radiation transmittable through the substrate while preventing any heat induced damage to the active epitaxial layers.
Film transfer to flexible substrates has been demonstrated by wet chemical etching of a sacrificial layer. This process relies on selective etching of a thin sacrificial layer grown below the epitaxial film. AlAs, and AlGaAs with a high aluminum content, are convenient sacrificial layers that can be used on GaAs substrates. The film and the flexible substrate are “peeled off” of the original substrate as the sacrificial layer dissolves in the etchant. High selectivity is achieved by a dilute HF etch of these materials. The etchant does not attack the GaAs substrate. Similar sacrificial layers and etch chemistries are also available for InP. However, the epitaxial film develops microcracks when transferred to a flexible substrate, and the subsequent processing is difficult on a non-rigid surface.
Thus, a need existed to provide a system and method to overcome the above problems.